Ce manuscrit présente l'étude d'une famille d'oxydes de chrome dans laquelle les composés peuvent être synthétisés selon deux phases qui présentent deux topologies différentes : les phases α-ACr₂O₄ (A=Sr, Ca, Ba) et β-CaCr₂O₄. Dans cette famille, les ions chrome portent un spin S=3/2 et forment soit des chaînes triangulaires, soit des plans triangulaires. Notre étude a donc été menée en deux parties : l'étude d'un système magnétique quasi-unidimensionnel et l'étude d'un système quasi-bidimensionnel.La première étude a été consacrée au composé β-CaCr₂O₄. Ce composé présente à basse température un comportement classique caractérisé par un ordre magnétique à longue portée associé à des corrélations 3D et au-dessus de la température d'ordre un comportement quantique caractéristique de chaînes de spins quasi-unidimensionnelles. L'objet de notre étude a donc été de mieux comprendre le mécanisme qui permet la transition d'un régime classique vers un régime quantique dans ce composé. Dans ce contexte nous avons exploré les effets de topologie et de contrainte structurale sur les propriétés magnétiques du composé, à travers l’étude de la série de composés substitués β-CaCr₂-xScxO₄ ainsi qu’une étude sur les effets de la pression. Ce travail a été mis en parallèle avec des calculs théoriques sur les chaînes de spins J₁-J₂.La seconde partie concerne le composé α-SrCr₂O₄. Notamment, l’étude par diffusion des neutrons de ce composé a mis en évidence l’influence de la dimension 2D ainsi que la distorsion du réseau triangulaire sur l’état fondamental du système et son comportement dynamique. / This thesis focuses on the study of a chromium oxide family in which the samples are synthsized into two forms with two different topologies : α-ACr₂O₄ (A=Sr, Ca, Ba) and β-CaCr₂O₄. In these compounds, the chromium ions carry a spin 3/2 and either form triangular spin chains or two dimensional triangular lattices. Our study was hence divided in two parts : the study of a quasi one-dimensional and of a two-dimensional antiferromagnet.The first part was dedicated to the β-CaCr₂O₄ compound. This system exhibits a classical behavior at low temperature associated to a three-dimensional long-range magnetic order and quantum properties typical of a spin chain above the Néel temperature.The aim o four study was therefore to understand the mecanism involved in this classical to quantum physics crossover.In this context, we explored the topological and structural effects on the magnetic properties of this system, through the study of the series of substituted compounds β-CaCr₂-xScxO₄, as well as a study of β-CaCr₂O₄ under pressure. This work was also supported by theoretical calculations on frustrated J₁-J₂ spin chains.The second part of this thesis focused on α-SrCr₂O₄. In particular, neutron scattering measurements on this compound highlighted the effects of the 2D character and the distortion of the triangular lattice on the ground state and dynamical properties in this system.

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本論文分為兩部分，第一部分探討使用OOMMF磁性材料模擬軟體來模擬奈米線波導中的自旋波特性，除了以往文獻所熱門的水平異向性薄膜合金中的自旋波，還模擬了垂直異向性的材料，我們模擬了在奈米線一端施加0 ~ 100 GHz外加磁場的自旋波響應。在模擬的結果中，我們發現了水平異向性與垂直異向性的重要差別，垂直異向性比水平異向性波導在頻率小於10 GHz時，少了複雜的自旋波傳遞。而在改變線寬的條件中，我們發現了垂直異向性波導在線寬夠大時，會因退磁場的效應，使得磁矩翻轉，形成許多磁壁，而水平異向性材料則不會，從水平異向性波導大於120 nm線寬的波型中，則會發現自旋波在波導中產生破碎的相位改變。而模擬具有水平寬度變化與垂直厚度變化的週期性邊界，則發現兩者所具有的濾波效果非常相似，而濾波的三個頻段，則是水平寬度變化所截止的頻段，寬於垂直厚度變化的頻段。 第二部分為 ，使用離子濺鍍製成總厚度200 nm，改變交錯層數的(Co/Pt)×N、(Co/Pd) ×N與(Pt/Pd) ×N，三種多層膜的磁性電性分析。Co/Pt與Co/Pd多層膜在Co厚度小於1 nm時為熱門垂直異向性材料，而本實驗專注於Co厚度大於1 nm時介面的特性以及兩種材料的差別。在磁阻的量測上面，得到不同於一般異向性磁阻的規律，一般的異向性磁阻的現象為，平行於電流施加磁場比垂直電流施加磁場所量測的電阻，前者電阻較大(ρ_(H∥I)>ρ_(H⊥I))，但是同為垂直於電流的平行於膜面磁場的電阻(ρ_(H⊥I,in-plane H))與垂直膜面磁場(ρ_(H⊥I,H perpendicular to plane))則呈現了不一樣的行為，尤其為垂直加場的部分，在某些條件的多層膜，會有明顯的垂直方向的異向性磁阻，是為介面所造成額外的垂直方向異向性磁阻，稱作”異向性介面磁阻”(Anisotropic Interface Magnetoresistance)。異向性磁阻與異性向介面磁阻都具有高電阻軸與垂直此軸的低電阻平面，而兩者差別在於異向性磁阻為電流方向軸，而異向性介面磁阻為膜面法向量軸，對於本實驗的量測方法來說，兩軸相差90度角，也因此可辨析兩者不同現象間的差異，並且在我們的分析之中發現，異向性介面磁阻在Co厚度為7 nm以下，才會明顯的顯現。 / The thesis is divided into two main parts. The first part discusses the properties of spin waves propagation in magnetic nanowire waveguide by micromagnetic simulation software OOMMF. In addition to in-plane magnetic anisotropy (IMA) in the thin film alloys, we simulate the perpendicular magnetic anisotropy (PMA) of the material. A transverse magnetic field is applied at one end of the waveguide wire and the frequency range is from 0 to 100 GHz. When frequency is less than 10 GHz, we observed that complex modes were generated in the IMA waveguide but there is no spin wave propagates in the PMA waveguide. We also studied the spin wave propagations in wires with different width. Irregular domain wall was generated by demagnetizing field in wider PMA waveguide but IMA waveguide does not have this behavior. In width-modulated and thickness-modulated waveguide spin wave simulations, these two filters have similar results with three band gaps from 0 to 100 GHz and the band gaps in width-modulated wire is wider than in thickness-modulated one. The second part is experimental measurements of the electrical and magnetic properties of (Co/Pt)×N, (Co/Pd) ×N, and (Pt/Pd) ×N multilayers, which are deposited by sputtering and the total thickness is 200nm. Co/Pt and Co/Pd were popular PMA materials when Co thickness is less than 1 nm. We focused on the multilayers with Co thicker than 1nm and the difference between these multilayers. In magnetoresistance measurement, the R-H curve is different from normal anisotropic magnetoresistance (AMR). AMR effect has different resistivity when H∥I or H⊥I, but the measurement results show that ρ_(H⊥I,in-plane H) and ρ_(H⊥I,H perpendicular to plane) also have different MR ratio in specific multilayer configuration. The effect is caused by the interface so it is anisotropic interface magnetoresistance (AIMR) as discussed in the literature. AMR and AIMR have both high resistivity axis and low resistivity plane which is perpendicular to the axis. The difference of two MRs is that the high resistivity axis is parallel to current in AMR and perpendicular to plane in AIMR. In the analysis, the AIMR effect is observed in multilayer with Co thickness less than 7 nm.